A catalytic converter is a device for converting harmful components included in exhaust gas into harmless components through catalysis. A general type of catalytic converter has a monolithic support in which a plurality of longitudinal channels is coated with slurry containing various catalytic components (hereinafter, referred to as “catalyst slurry”). The monolithic support is made of ceramic or other materials. Various methods of coating a monolithic support with catalyst slurry are commonly known in the related field.
As indicated in U.S. Pat. No. 6,599,570, it is proposed that a vacuum is used in order to draw catalyst slurry upward through channels. For example, it is disclosed in U.S. Pat. No. 4,384,014 that, in order to remove air from channels, catalyst slurry is drawn upward through the channels by generating a vacuum over a monolithic support. Thereafter, the vacuum is released, and thus excessive catalyst slurry is removed by gravity discharge. Further, it is disclosed in U.S. Pat. No. 4,191,126 that a monolithic support is dipped into slurry, thus removing excessively-applied slurry from the surface of the monolithic support using pressure lower than atmospheric pressure.
Most of all, U.S. Pat. No. 4,609,563 is particularly noticeable. U.S. Pat. No. 4,609,563 discloses a metered charge system for catalytic coating of a substrate. This system includes a method of coating a ceramic monolithic support with a precisely-controlled predetermined amount (hereinafter, “quantitatively-determined amount”) of catalyst slurry using a vacuum. Briefly explaining, the monolithic support is immersed into a quantitatively-determined amount of slurry (to be applied on the support) charged in a predetermined size container to a predetermined depth. In this case, the slurry is drawn by the vacuum applied to the end of the support opposite to the immersed end thereof. Therefore, it is expected that it is not required to discharge or remove excessive slurry from a substrate. However, even in this case, it is likely that it is difficult to coat the monolithic support with a precisely quantitatively-determined amount of slurry such that the profiles of channels in the monolithic support are uniform.